It does depend on where you are going from and going to to the cost. The ferry company's do differ. They do add on vat as well . I found my trailer and 4x4 was just longer than my lorry so the crossing was cheaper by lorry. My trailer and 4 x 4 was just over 8 metres. You could always use a company like Equine Logistics to sort it out for you, they can end up with better deals and takes the worry from you. PM me if you want their details.